The invention pertains to a ceramic material, as well as a method of making the same, that contains silicon aluminum oxynitride (SiAlON) and a rare earth constituent.
SiAlON materials have a number of uses such as, for example, cutting inserts for various metal cutting application and wear parts for various wear applications (e.g., plunger rods for pumps, plunger ball blanks, down hole pump check valve blanks, bushings, blast nozzles, and other wear and impact applications). Exemplary patents that disclose SiAlON materials are U.S. Pat. No. 4,563,433 to Yeckley and U.S. Pat. No. 4,711,644 to Yeckley, as well as U.S. Pat. No. 6,693,054 to Yeckley. One article that discusses SiAlON materials is Izhevskiy et al., “Progress in SiAlON ceramics, Journal of the European Ceramic Society 20 (2000) pages 2275-2295.
SiAlON materials may contain an alpha prime (or alpha') phase and a beta prime (or beta') phase and one or more other phases such as, for example, a glassy phase and/or a crystalline phase. The alpha prime SiAlON phase may be of the formula MxSi12-(m+n)Alm+nOnN16-n where M is Li, Ca, Y, Mg or other lanthanides and where the theoretical maximum of x is 2, the value of n ranges between greater than 0 and less than or equal to 2.0, and the value of m ranges between greater than or equal to 0.9 and less than or equal to 3.5. The beta prime SiAlON phase may be of the formula Si6-zAlzOzN8-z where 0<z≦4.2.
The above-mentioned U.S. Pat. No. 6,693,054 to Yeckley discloses a SiAlON material that contains an alpha prime SiAlON phase and a beta prime SiAlON phase. This ceramic material has a ytterbium addition so that the alpha prime SiAlON phase has the formula YbX Si(m+n) AlmOnN16m. In some instances, there was a glassy phase or a crystalline phase that was present. Further, U.S. Pat. No. 6,693,054 to Yeckley discloses a process to make the alpha-beta SiAlON containing ytterbium using a silicon nitride starting powder that contains either no or a low amount (i.e., an amount that has a lower limit equal to zero weight percent and an upper limit equal to about 1.6 weight percent) of beta silicon nitride.
SiAlON materials may comprise an alpha prime SiAlON phase and a beta prime SiAlON phase, as well as further contain silicon carbide particles dispersed throughout the SiAlON matrix. Such a SiAlON material is disclosed in U.S. Pat. No. 4,826,791 to Mehrotra et al.
U.S. Pat. No. 5,370,716 to Mehrotra et al. discloses a high Z-SiAlON material comprising beta prime SiAlON phase. The beta prime SiAlON phase has a formula Si6-zAlzOzN8-z where 1<z<3.
U.S. Pat. No. 5,908,798 to Chen et al. discloses a SiAlON ceramic that has a relatively high proportion (i.e., greater than any other phase present) of alpha prime SiAlON. The '798 Patent to Chen et al. lists the following additives: Li, Mg, Ca, Y, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, or mixtures thereof. The more preferably additives are Nd, Yb, Sm, Y, Li, or mixtures thereof. Each one of the examples of the '798 Patent to Chen et al. appears to use only one of the additives identified in the listing. The '798 Patent to Chen et al. appears to use a starting silicon nitride powder that comprises about 93 weight percent beta silicon nitride and about 7 weight percent alpha silicon nitride. Chen et al. does not appear to address a SiAlON ceramic that is made from a starting powder mixture that includes silicon nitride starting powder that contains either no or a low amount of (i.e., an amount that has a lower limit equal to zero weight percent and an upper limit equal to about 1.6 weight percent) beta silicon nitride.
U.S. Pat. No. 5,413,972 to Hwang et al. discloses a substantially glass-free alpha-beta SiAlON ceramic material that includes an additive that is the cationic element M in the alpha-SiAlON phase with the formula: Mx(Si,Al)12(O,N)16 wherein 0<x<2. These additives are Sr, Ca, Mg, Li, Na, Ce, Y, Nd, Sm, Gd, Dy, Er, and Yb. The specific examples use yttrium (Y) and strontium (Sr) added as their oxides to the starting powder mixture. The silicon nitride starting powder is from UBE Industries, Inc. and available under the designation SNE-10. The Tien et al. patent states that the β/(α+β) ratio for SNE-10 is less than 5 percent. Applicant believes that SNE-10 silicon nitride powder from UBE Industries, Inc. contains about 2 weight percent beta silicon nitride with the balance comprising alpha silicon nitride along with unavoidable impurities. The '972 Patent to Hwang et al. does not appear to address a SiAlON ceramic that is made from a starting powder mixture that includes silicon nitride starting powder that contains either no or a low amount of (i.e., an amount that has a lower limit equal to zero weight percent and an upper limit equal to about 1.6 weight percent) beta silicon nitride.
U.S. Pat. No. 6,124,225 to Tien et al. discloses a SiAlON ceramic material that has a high proportion of alpha prime SiAlON. Tien et al. lists the following additives Nd, Sm, Gd, Dy, Yb and Y and mixtures thereof with Gd being the preferred additive. In one preferred embodiment, the starting silicon nitride powder has about 95 weight percent alpha silicon nitride. The '225 Patent to Tien et al. does not appear to address a SiAlON ceramic that is made from a starting powder mixture that includes silicon nitride starting powder that contains either no or a low amount of (i.e., an amount that has a lower limit equal to zero weight percent and an upper limit equal to about 1.6 weight percent) beta silicon nitride.
U.S. Pat. No. 5,200,374 to Yamada et al. discloses an alpha-beta SiAlON ceramic material. The '374 Patent to Yamada et al. lists a number of the additives as follows: Ho, Er, Tm, Yb or Lu wherein the examples appear to use only one additive. The starting powders appear to include alpha-SiAlON powder and a silicon nitride powder that appears to have properties like those of the Ube Industries SNE-100 powder wherein applicant believes that the UBE-100 silicon nitride powder contains about 2 weight percent beta silicon nitride with the balance comprising alpha silicon nitride along with unavoidable impurities. The '374 Patent to Yamada et al. does not appear to address a SiAlON ceramic that is made from a starting powder mixture that includes silicon nitride starting powder that contains either no or a low amount of (i.e., an amount that has a lower limit equal to zero weight percent and an upper limit equal to about 1.6 weight percent) beta silicon nitride.
Japanese Patent Publication No. 5-43333 to UBE Industries lists Ho, Er, Tm, Yb and Lu as additives for a SiAlON ceramic material. The examples appear to use only one additive. This Japanese Patent Publication does not appear to address a SiAlON ceramic that is made from a starting powder mixture that includes silicon nitride starting powder that contains at least 2 weight percent and possibly a greater content of beta silicon nitride.
The Shen et al. article (Journal of the European Ceramic Society 16 (1996) pp. 873-883) entitled “Reactions Occurring in Post Heat-Treated α/β Sialons: On the Thermal Stability of α-SiAlON” lists the following elements that are used alone: Nd, Sm, Dy and Yb. The starting silicon nitride powder was identified in the article as UBE SN-E10. There does not appear to be any teaching in the Shen et al. article directed to a SiAlON ceramic that is made from a starting powder mixture that includes silicon nitride starting powder that contains either no or a low amount of (i.e., an amount that has a lower limit equal to zero weight percent and an upper limit equal to about 1.6 weight percent) beta silicon nitride.
The Wang et al. article (Journal of the European Ceramic Society 13 (1994) pp. 461-465) entitled “Preparation of R-α′β′-Sialons (R═Sm, Gd, Dy, Y and Yb) by Pressureless Sintering” lists the following elements: Sm, Gd, Dy, Y and Yb. The examples appear to show these elements used alone and not in combination with one another. The kind of silicon nitride starting powder appears to be unknown since it was laboratory and contains 1.5% oxygen. In the Wang et al. article, there does not appear to be any teaching directed to a SiAlON ceramic that is made from a starting powder mixture that includes silicon nitride starting powder that contains either no or a low amount of (i.e., an amount that has a lower limit equal to zero weight percent and an upper limit equal to about 1.6 weight percent) beta silicon nitride.
The Nordberg et al. article (J American Ceramic Society 81 [6] pp. 1461-70 (1998)) entitled “Stability and Oxidation Properties of RE-α-Sialon Ceramics (RE=Y, Nd, Sm, Yb)” discloses that alpha-SiAlON can be formed using additives. The examples appear to use only one rare earth element (e.g., Nd, Sm, or Yb). The article describes the starting silicon nitride powder as UBE, SN-E10. There do not appear to be any teaching about a SiAlON ceramic that is made from a starting powder mixture that includes silicon nitride starting powder that contains either no or a low amount of (i.e., an amount that has a lower limit equal to zero weight percent and an upper limit equal to about 1.6 weight percent) beta silicon nitride.
U.S. Pat. No. 4,547,470 to Tanase et al. discloses either yttrium alone or erbium alone as an additive in the SiAlON, and discloses the use of zirconium in the form of zirconium carbonitride in connection with a SiAlON. The starting silicon nitride powder comprises 90 volume percent alpha silicon nitride. The '470 Patent to Tanase et al. does not appear to address a SiAlON ceramic that is made from a starting powder mixture that includes silicon nitride starting powder that contains either no or a low amount of (i.e., an amount that has a lower limit equal to zero weight percent and an upper limit equal to about 1.6 weight percent) beta silicon nitride.
Japanese Patent No. 2,988,966 to Hitachi Metals Co. Ltd. discloses an alpha-beta SiAlON that includes an element selected from Y, Er and Yb. Only one examples uses two elements (Er and Yb). The starting silicon nitride powder has an alpha conversion ratio equal to 93% so that it equate to a powder that contains 7 weight percent beta silicon nitride.
Japanese Patent Publication 4002664A, based on an English abstract, discloses a SiAlON ceramic that can use the following elements: Ho, Er, Tm, Yb or Lu that are used along with Hf or Zr. This Japanese document does not address a SiAlON ceramic that is made from a starting powder mixture that includes silicon nitride starting powder that contains either no or a low amount of (i.e., an amount that has a lower limit equal to zero weight percent and an upper limit equal to about 1.6 weight percent) beta silicon nitride.
Although current SiAlON ceramic bodies, such as for example, cutting inserts exhibit acceptable properties (e.g., hardness, toughness, thermal shock resistance) it would be desirable to provide for an improved SiAlON material that has application as a cutting insert that exhibits improved metal cutting performance properties including hardness, Young's modulus, toughness, thermal conductivity, and thermal shock resistance. The same is true for SiAlON wear parts in that although current SiAlON wear parts have acceptable properties (e.g., hardness, Young's modulus, toughness, thermal conductivity, and thermal shock resistance), it would be desirable to provide an improved SiAlON material that has application as a wear part that exhibits improved properties.
In this regard, in the sintering of a powder mixture to make SiAlON material, crystalline phases can form in the grain boundaries between the alpha prime SiAlON grains and the beta prime SiAlON grains. An increase in the content of crystalline phases in the grain boundaries can result in a reduction of the fracture toughness of the SiAlON material. Hence, it would be desirable to provide a SiAlON material that has a minimal amount of the crystalline phase(s) that have formed in the grain boundaries.
The temperature at which the additives form a liquid phase can impact upon the densification of the SiAlON body. In order to improve the densification of the SiAlON body, it would be advantageous to use additives that form a liquid phase at a relatively lower temperature.
Along this same line, it would be advantageous in regard to the formation of the alpha prime SiAlON phase to use additive(s) that would form and maintain an intergranular liquid phase upon sintering and throughout the sintering cycle (i.e., a non-binding liquid phase-forming additive). In this situation, essentially none of the non-binding liquid phase-forming additives would become a part of the alpha prime SiAlON phase ,i.e., there would be essentially no detectable amount of the non-binding liquid phase—forming additive in the alpha prime SiAlON phase. More specifically, what this means is that in the case where the grains of the alpha prime SiAlON phase are sufficiently large (i.e., on the order of greater than or equal to about 2 micrometers in diameter) one does not detect the presence of such non-binding liquid phase-forming additives in the grains of the alpha prime SiAlON phase through the use of energy dispersive spectrum-scanning electron microscopy (EDS/SEM) techniques. The result of the absence of any detectable amount of non-binding liquid phase-forming additive in the alpha prime SiAlON phase would be that the liquid phase would be maintained through the sintering cycle. By maintaining the liquid phase during the sintering cycle, the amount of alpha prime SiAlON phase that would be formed increases. Applicant believes that it would be desirable to provide a SiAlON ceramic body that has an increased content of alpha prime SiAlON phase.
SiAlON ceramic material that exhibits a higher hardness has advantages for use in certain applications as a cutting insert and as a wear part. Typically, a SiAlON ceramic material that has a finer grain size results in a higher hardness. Thus, it would be desirable to provide a SiAlON ceramic material that has a finer grain size, and hence, a higher hardness.